I'll be getting new wheels in the near future and I came across this site in my searches:
http://www.tuneruniversity.com/blog/...n-performance/
Read through parts 1 and 2 as well, but part 3 relates to width specifically. There's also a calculator he provides
here that you can type in wheel and tire sizes you're thinking about and see if they'll fit.
Don't know if anyone else has ran across this site, but it's super good info!